This invention relates to a process for the treatment of wastewater containing sour gases, for example, SO.sub.2, H.sub.2 S, and/or CO.sub.2, and in particular to a process wherein the wastewater is stripped with a stripping gas, and the resultant stripping gas containing the sour gases is introduced into a combustion stage.
Wastewater containing sour gases is formed in many scrubbing processes directed to waste gas purification, inasmuch as a water scrubbing step normally takes place prior to the main physical or chemical scrubbing step. Besides cooling the waste gas, this water scrubbing step also provides for effective preliminary purification. During the water scrubbing step the temperature drops far below the H.sub.2 O dewpoint of the waste gas. Therefore, a substantial proportion of the water vapor contained in the waste gas is condensed. Depending on whether the waste gas has already been prepurified, for example, in a Claus facility, the water vapor may also constitute water of reaction which, in order to increase the yield, is removed prior to the actual sour gas scrubbing operation.
In a conventional process of this type, a gas rich, for example, in H.sub.2 S is fed into a Claus furnace and subsequently undergoes an incineration stage as well as an SO.sub.2 scrubbing operation. In this procedure, an SO.sub.2 -containing wastewater is removed from the bottom of the preliminary water scrubbing column, and this wastewater must not be discharged without treatment.
It is also known that oil refineries and coke oven plants often produce wastewater that contains sour gases. Thus, numerous refinery gases, liquids, and coke oven gases which come into contact with water and/or steam during their various conversion processes, result in so-called "sour water". This contaminated water contains, among other components, ammonia and hydrogen sulfide in dissolved form and, therefore, can never be directly discharged.
There are various procedures for treating sour wastewaters to make them sufficiently nonpolluting. For example, the wastewaters from water scrubbing stages provided upstream of SO.sub.2 and H.sub.2 S scrubbing operations are frequently treated by means of neutralization and sedimentation. However, the drawbacks of this procedure are that large quantities of salt must be transported, and the water, subsequently discharged into a main sewer system, has a higher chemical oxygen demand (COD), since it contains reaction products, for example, sulfides, sulfites, and/or sulfates of calcium or sodium.
Another conventional process for the treatment of wastewater containing sour gases is to strip the wastewater by means of a gas and then feed the resultant gas containing the sour gases into a combustion stage. Suitable stripping gases in this connection are steam, air, and other O.sub.2 -containing gases. In addition to the stripping gas, conventional processes also generally require the use of supplemental air or some other O.sub.2 -containing gas in order to ensure an optimum reaction in the combustion stage, as described in U.S. Pat. No. 3,821,110.
In order to obtain wastewater of maximum purity, sufficiently large quantities of stripping gas and equipment to handle same are necessary. This can have an adverse effect on the economy of the process. On the other hand, if a lesser amount of stripping gas is used, wastewater that is more polluted is discharged into the sewer system. Moreover, the type of incorporation of the wastewater treatment within the total process is not optimal with respect to initial outlay and operating costs.